The Broader Significance of NEOs

excerpted from:

Report of Near-Earth Object Survey Working Group.  

E. M. Shoemaker, G. Canavan, J. Darrah, A. Harris, D. Morrison,
M. Mumma, D. Rabiniwitz, J. Rahe, C. Chapman, B. Marsden, S. Ostro,
and D. Yeomans (1995).
[NASA Report. Available at http://impact.arc.nasa.gov/reports.html]
--------------------------------------------------------------------

XI. The Broader Significance of NEOs 

The NEO survey recommended here constitutes a fiscally sensible first
step in assessing and reducing the risk of a globally catastrophic
asteroid or comet collision with Earth. The most likely, and certainly
the most desirable outcome of the survey, will be that none of the
discovered NEOs will turn out to be hazardous during at least the next
century. Regardless of the outcome, the survey will identify tens of
thousands of small worlds that, at least for a century, are not on
collision course with Earth.

The potential promise of these "friendly" NEOs is highly significant
for a variety of reasons, most of which stem from their closeness to
Earth and their accessibility. The NEO population includes the
cheapest targets of human and robotic exploration beyond the
Earth-Moon system. In fact, many of the objects likely to be
discovered will be accessible with very low delta V (i.e., less than
required to land on the Moon and for only those with small orbital
eccenticities) and low roundtrip mission times (6 months or
less). These represent by far the easiest targets for human
exploration (far easier than landing on the Moon - no landing module
required, minimal delta V for rendezvous and escape).

Therefore, expeditions to NEOs are logical next steps in an
evolutionary program of human exploration of the solar system: The
NEOs are humanity's stepping stones to Mars and ultimately deeper
space. Of course, any economically viable vision of space exploration
will place the highest immediate priority on inexpensive robotic
including multiple flyby, rendezvous, and sample return. High-speed
intercept of numerous NEOs by microsatellites also appears feasible
and cost-effective.

The rationale for telescopic and robotic reconnaissance of NEOs is
multifaceted. Pieces of NEOs that have fallen to Earth as meteorites
show a wide diversity of composition. Most contain at least some free
metal (iron-nickel alloy and small portions of platinum-group metals
and gold) and chemically-bound oxygen. Many contain organic chemicals
and water of hydration. The NEOs thus constitute key space resources
with considerable potential in the future exploration of space. In
principal, NEO minerals could be used to provide oxygen, water,
biomass, and fuel to help sustain human colonies. Many NEOs may be
loosely bound aggregates that would facilitate construction of a human
habitat within a shell of material to secure shielding from
potentially lethal high-energy particles. In this light, NEOs may
ultimately become the first long term human outposts beyond the
Earth-Moon system.

Meanwhile, it is desirable to begin to build up a base of knowledge
for deflecting or destroying a threatening object; thorough
understanding of the internal structure of NEOs will require robotic
exploration and may require geophysical reconnaissance by
humans. Fortunately, the likely sizes of accessible NEOs are well
suited to the capabilities of human explorers.

The recent discovery that we exist in an asteroid swarm has enormous
long term consequences, and its historical importance may someday be
seen to rank with Columbus's discovery of the New World. Collisions
with NEOs have played a prominent role in the geological and
biological evolution of Earth, and one way or another, NEOs probably
will play a role in the long term future of human civilization. Our
knowledge of the NEO population (and of its influence on the origin
and evolution of Earth and life) is in its infancy, and detailed
information about individual objects is extremely sparse. However, a
science of NEOs has emerged, and can be expected to mature in parallel
with the discovery and exploration of the NEO population.

It is thought that the NEO population is derived from a great range of
sources -- primitive asteroids, differentiated asteroids, and extinct
comets. Probably they include everything from returning fragments of
Earth-Venus planetesimals to Uranus-Neptune planetesimals and Kuiper
belt objects. Because of their frequent close passes by the
terrestrial planets, the dynamical evolution of NEOs is extremely
complex. Definition of the orbits of a sufficiently large sample of
NEOs is likely to elucidate mechanisms for their delivery into
Earth-crossing orbits and should also refine statistical assessments
of collision probabilities. This work is coupled to determination of
cratering rates and the chronology of evolution of the terrestrial
planets. It also should constrain ideas about delivery of volatiles to
Earth and the terrestrial planets and the influence of this process on
the early history of life.

During the past few decades, NASA's discovery and exploration of other
worlds has captured the imagination of a generation of young people
who decided to embark on careers in science and engineering. These
achievements of America's space program have truly elevated the human
spirit. History tells us that the need to explore is built into the
human psyche. Most would agree that an exciting, yet affordable,
domestic space program can help to ensure the vitality of our society
as we begin the next millennium. All indications from telescopic
observations are that many NEOs are unlike any objects yet seen by
spacecraft, extraordinarily strange places that pose unique challenges
for investigations by robots and humans.

Accordingly we recommend that NASA view the NEO survey as part of a
broad-based program of NEO research focused on robotic and human
exploration objectives. NASA should embrace discovery and exploration
of Earth-crossing asteroids as a cornerstone of the space program, as
a fiscally responsible initiative with virtually enormous guaranteed
return.

The United States could celebrate the dawn of the Third Millennium by
declaring its intention to land humans on an asteroid to conduct
intensive scientific exploration and to return them safely to Earth in
the first decade of the next century.

Note Added in Press by Near-Earth Objects Survey Working Group on 
30 June 1995: This study was conducted under severe time restrictions,
thus it was not possible to consider certain aspects that would
otherwise have been explored more thoroughly. In particular, the
Working Group did not consider surveys from space. Proper study of
space-based surveys would have required more resources and time than
were available to the Working Group, and are therefore deferred to a
future study.

Likewise, it must be stated that the plan outlined in this report does
not fully address the hazards posed by comets, especially long-period
ones and dormant nuclei. This matter deserves further study, both in
terms of the level of hazard posed and in effective means of detection
of such objects.

This report deals primarily with scientific and technical issues
related to near-term assessment of the impact hazard, within the
constraints imposed by a severe fiscal environment. However, in this
section we briefly consider certain other aspects of near-Earth
objects, primarily from the perspective of future exploration and
exploitation. The Study Group presents these as interesting
possibilities with varying degrees of practicality, ranging from
`presently economically and technically feasible' in the case of
robotic exploration to `provocative and interesting' in the case of
resource extraction. Clearly, the most significant dividend from
near-term exploration of near-Earth objects will be improved
understanding of the roles played by such objects in the origin and
evolution of our planetary system, and their influence on humans and
other living organisms.